This application is based on Japanese Patent Application 2002-141153, filed on May 16, 2002, the entire contents of which are incorporated herein by reference.
A) Field of the Invention
This invention relates to a solid-state imaging device having on-chip microlenses.
B) Description of the Related Art
FIG. 10 are enlarged cross-sectional views showing a part of a conventional solid-state imaging device.
On a surface of a semi-conductor substrate 1 made of n-type silicon or the like, p-type wells are formed. On a surface region of each p-type well, an n-type region 2 and an n-type transfer channel region 3 forming a photoelectric conversion unit (a photodiode) of a p-n junction diode structure. A separating (channel stop) region 4 electrically separating the n-type region 2 and the n-type transfer channel region 3 of the photodiode is formed of a p-type region. The surface of the semi-conductor substrate 1 on which the photodiodes 2, the transfer channel region 3 and the separating region 4 are formed are oxidized to form an insulating film 5 made of a silicon oxide film or the like.
Next, above each transfer channel region 3, a transfer electrode 6 made of double-layer poly-silicon (double poly-silicon) are formed and covered with an insulating film 5a. On the insulating film 5a, a light shading film 7 made of tungsten (W) or the like and having an opening above each of the photodiodes 2 are formed.
On the light shading film 7, a first planarizing layer 8 including a passivation layer and a planarizing insulating layer is formed. On the first planarizing layer 8, a color filter layer 9 consisted of filters of three colors: red (R), green (G) and blue (B). On the color filter layer 9, a second planarizing layer 10 that is transparent insulator such as a photoresist or the like is formed by spin-coat or the like in order to planarize the surface.
On the second planarizing layer 10, a resist layer is formed and are patterned to make microlens patterns 11a by photolithography or the like.
As shown in FIG. 10B, microlenses 11 are formed by flowing the microlens patterns 11a. 
All of the above-described microlenses 11 are formed at once under the same condition in order to make their forms equal. Therefore, giving different characteristics to individual microlenses 11 is not performed.
Recently, by miniaturization of a pixel, a radius of the microlens 11 becomes smaller and a focal distance of the microlens 11 becomes shorter as a result; therefore, a focal point will be between the microlens 11 and the surface of the photodiode 2. Therefore, it is necessary to make a distance between the microlens 11 and the surface of the photodiode 2 shorter. In order to make it, it is desired to thin either one of the first planarizing layer 8, the color filter layer 9 and the second planarizing layer 10 formed between the microlens 11 and the surface of the photodiode 2.
The color filter layer 9 cannot be thinned because of necessity of keeping spectral characteristics. That is, if the color filter layer 9 is thinned, color reproductivity is lowered due to mixture of light of wavelength which should not be go through the color filter layer 9. In other words, a color that is not a color of the filter will be mixed in the color of the filter.
If the first planarizing layer 9 formed under the color filter layer 9 is thinned, it is difficult to eliminate steps. Moreover, when the color filter layer 9 is made of a pigment dispersed type colored resist, the color filter layer 9 will be closer to the surface of the photodiode 2 because of the thinning of the first planarizing layer 9. Therefore, grain radius of the pigment will be optical shadows (spots). By the shadows, sensitivity gaps are generated in the photodiode 2 and an image by the photodiode 2 will have grittiness.
The color filter layer 9 is formed colors by colors. That is, the color filter layer 9 is made of a three-color, for example red (R), green (G) and blue (B), mosaic patterned color filter formed by repeatedly patterning on the same plan. At this time, it is difficult to avoid gaps generated by overlapping of the filters at boundaries of each color filter. In order to eliminate the gaps, the second planarizing layer 10 should be formed over the color filter layer 9. It can be considered that the second planarizing layer 10 is omitted to shorten the distance between the microlens 11 and the surface of the photodiode 2. However, if the second planarizing layer 10 is omitted, formation of a high quality microlens will be difficult because the gaps are not eliminated.
It is an object of the present invention to provide a solid-state imaging device having good spectral sensitivity when a pixel is miniaturized.
Also, it is another object of the present invention to provide a solid-state imaging device having ideal color reproductivity with keeping high sensitivity.
According to one aspect of the present invention, there is provided a solid-state imaging device, comprising: a semi-conductor substrate demarcating a two-dimensional surface; a multiplicity of photoelectric conversion units formed being arranged in a plurality of rows and columns on the semiconductor substrate; a planarizing insulating film formed above the semiconductor substrate; and a plurality of gap-less microlenses having spectral characters, each gap-less microlens being formed above each of the photoelectric conversion units with the planarizing insulating film placed in-between.
According to another aspect of the present invention, there is provided a solid-state imaging device, comprising: a semi-conductor substrate demarcating a two-dimensional surface; a multiplicity of photoelectric conversion units formed being arranged in a plurality of rows and columns on the semiconductor substrate; a planarizing insulating film formed above the semiconductor substrate; a plurality of inner-lenses having spectral characters, each inner-lens corresponding to each of the photoelectric conversion units; and a plurality of gap-less microlenses made of a transparent resist, each gap-less microlens being formed above each of the photoelectric conversion units with the planarizing insulating film and the inner lenses placed in-between.
According to further aspect of the present invention, there is provided a manufacturing method of a solid-state imaging device, comprising the steps of: (a) preparing a semi-conductor substrate demarcating a two-dimensional surface; (b) forming a multiplicity of photoelectric conversion units arranged in a plurality of rows and columns on the semiconductor substrate; (c) forming a planarizing insulating film above the semiconductor substrate; and (d) forming a plurality of gap-less microlenses having spectral characters, each gap-less microlens being formed above each of the photoelectric conversion units with the planarizing insulating film placed in-between.
According to the present invention, a solid-state imaging device having good spectral sensitivity when a pixel is miniaturized can be provided.